About Extruding Faces
Ok, i chose those faces and unjoined from rest of mesh and tried again. This time it worked. So it must be faces, next to them, causing the problem. But when i unjoined and extruded those faces, shading looked alittle weird. Also i didn't want to apply solidify to the whole mesh to prevent from unnecessary polygons. In the end, this is what i made.

I made over the mesh.

1.I applied solidify on a basic cylinder



2.Then gave details to outer face only and my problem seems to have fixed